Genetic differences between populations of sardine, Sardina pilchardus, and anchovy, Engraulis encrasicolus, in the Aegean and Ionian seas

Genetic distances based on electrophoretic variation and multivariate analysis of several morpho‐metric and meristic characters suggest that populations of sardine and anchovy from the Aegean and Ionian seas do not form one panmictic population. The distinction between these two classes of populations emerges only as a statistical property, and for some characters the within‐sea variation is larger than the between‐sea variation. Thus, the reproductive isolation between populations inhabiting the two seas appears to be only partial. Our findings do not support the‘ pure‘ or‘ discrete‘ stock concept. Instead, they provide evidence for the dynamic population structure model according to which physical (e.g., hydrographic) or biological (e.g., predation or behaviour) factors impose a population structure maintained in a semi‐equilibrium state under the opposing influences of migration and selection. Such a dynamic state may not be stable in the long run, and it may not allow for the accumulation of genetic divergence necessary for the emergence of higher taxa. It must, nevertheless, be taken into account in the management of exploited natural populations.